Horton

Re: COUNT(*) again (was Re: [HACKERS] Index/Function organized

Bruce Momjian <pgman@candle.pha.pa.us>

View thread View on postgr.es
From: Bruce Momjian <pgman@candle.pha.pa.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Hannu Krosing <hannu@tm.ee>, Christopher Browne <cbbrowne@libertyrms.info>, pgsql-performance@postgresql.org, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2003-10-05T13:36:40Z
Lists: pgsql-hackers, pgsql-performance 
Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Tom Lane wrote:
> >> I think that's not happening, conditionally or otherwise.  The atomicity
> >> problems alone are sufficient reason why not, even before you look at
> >> the performance issues.
> 
> > What are the atomicity problems of adding a create/expire xid to the
> > index tuples?
> 
> You can't update a tuple's status in just one place ... you have to
> update the copies in the indexes too.

But we don't update the tuple status for a commit, we just mark the xid
as committed.  We do have lazy status bits that prevent later lookups in
pg_clog, but we have those in the index already also.

What am I missing?

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073